Reliable via structures having hydrophobic inner wall surfaces

ABSTRACT

Disclosed is a method of making a reliable via hole in a semiconductor device layer, and a reliable via structure having internal wall surface layers that are hydrophobic, and thereby are non-moisture absorbing. The inner wall of the via structure has a layer of material having a characteristic of spin on glass (SOG), such that the characteristic is that the outer layer of the SOG oxidizes during photoresist ashing to form a surface layer of silicon dioxide in the via hole wall. In the method, the via structure is placed through a chemical dehydroxylation operation after the ashing operation, such that the layer of silicon dioxide in the via hole wall is converted into a hydrophobic material layer. The conversion is performed by introducing a halogen compound suitable for the chemical dehydroxylation operation, wherein the halogen compound may be NH 4 F or CCl 4 .

This application is a division of Ser. No. 09/234,235 filed Jan. 20,1999, now U.S. Pat. No. 6,165,905.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to reliable semiconductor via structures,and more particularly, the present invention relates to techniques forconverting silicon dioxide layer regions within via hole walls intomoisture repellant hydrophobic layer regions.

2. Description of the Related Art

In the fabrication of semiconductor devices, various layers are providedwith conductive material, such as metal lines. The metal lines arecommonly formed over successive insulating dielectric layers.Accordingly, it is generally necessary to electrically interconnect themetal lines between the dielectric layers. To accomplish this, vias (orvia holes) are formed through the dielectric layers to electricallyinterconnect selected metal lines or features.

Spin on glass material (“SOG material”) is used for some of thedielectric layers. For example, so-called “true” SOG materials, such asthat sold under the brand name “LSU 418,” which is available from AlliedSignal, Inc. of Sunnyvale, Calif., is used because it has a low kcharacteristic (e.g., dielectric constant less than 4.0, which is commonfor silicon dioxide). Many “SOG-like” materials also have a low kcharacteristic. The SOG-like materials may, for example, be spin coatedor result from vapor deposition using methyl silane and hydrogenperoxide chemistry. However, both the true SOG materials and theSOG-like materials oxidize during and after an operation known asashing. Ashing is commonly performed to remove a photoresist layer thathas been spin coated over the SOG material to facilitate patterningoperations. Unfortunately, the oxidized SOG materials are known toabsorb too much moisture from the atmosphere, in that during lateroperations (such as, for example, during metal deposition), the absorbedmoisture outgasses causing poisoning of the vias. Such poisoningprevents adequate electrical connections from being made, e.g., betweenthe opposite metal layers which are to be interconnected by way of theconductive material in the vias.

Unfortunately, prior art attempts to reduce the amount of the moistureretained by the oxidized SOG materials have not been successful. Forexample, if thermal outgassing is performed at a high enoughtemperatures to remove adequate amounts of the moisture (e.g., at about700 degrees C.) from the oxidized SOG materials, significant problemsresult. These high outgassing temperatures are generally considered tooexcessive for the metal layers to withstand without causing damage(e.g., metal layers of aluminum may deform). Also, the SOG material isnot stable at the high outgassing temperatures. If lower temperaturesare used in an attempt to reduce the moisture retained by the oxidizedSOG materials (e.g., at 400 to 450 degrees C. in a PVD chamber),although the metal lines may not be damaged by the temperature, notenough of the moisture is removed. The remaining moisture then outgassesduring later attempts to deposit via coating/filling materials such astitanium nitride (TiN) and tungsten (W) metal layers (which are commonlyused for the conductive vias), and such outgassing prevents propercontinuous deposition of these metal layers in the internal via walls.For example, the outgassing moisture may prevent tungsten from beingdeposited on the walls of the via, and the TiN will tend to depositdiscontinuously (e.g., in separate random groups), rather than in acomplete conductive layer.

To facilitate this discussion, FIG. 1A shows a semiconductor structureincluding a substrate 101 supporting a first conductor 102, such as ametal line, which is to be in contact with a second conductor 103, suchas a conductive layer of titanium nitride shown in FIG. 1C. Deposited onthe substrate 101 is a layer 104 of SOG material, which may include bothtrue SOG materials, materials having a SOG-like characteristic, andother organic low-K dielectric materials. Accordingly, suchcharacteristic includes having a low dielectric constant (K), andoxidizing during photoresist ashing to form a surface layer 106 ofsilicon dioxide. After deposition of a silicon dioxide layer 107 on thelayer 104 of SOG material, a via hole 109 is formed through the silicondioxide layer 107 and through the SOG material layer 104 to expose themetal 102 as shown in FIG. 1A.

Between the etching operation and a subsequent deposition operation, asemiconductor structure 111 defined by the substrate 101 and the layers102, 104, and 107, is exposed to oxygen in the atmosphere. The oxygenthus causes the inner wall surface of the via hole 109 to oxidize andform the surface layer 106. As described above, the surface layer 106 isvery porous, is prone to collect moisture, and upon being heated,releases gaseous moisture.

The effect of the release of the moisture is shown in FIG. 1C, whichdepicts operations intended to deposit a layer 103 of titanium nitrideunder a layer 114 of tungsten. The purpose of the titanium nitride layer103 is to electrically interconnect the first conductor 102 to thetungsten layer 114. However, FIG. 1C shows arrows 116 depicting moisturebeing outgassed from the surface layer 106 during the deposition of thetitanium nitride layer 103. The outgassed moisture prevents the layer103 of titanium nitride from being continuous, as illustrated by thespaced pieces 103 a of titanium nitride. It may be understood, then,that the word “layer” in the phrase “layer 103” denotes the desired formof the titanium nitride, whereas the actual form of the prior arttitanium nitride layer is discontinuous as shown in FIG. 1C. Because thepieces 103 a are spaced, the desired electrical interconnection from themetal 102 to the tungsten 114 is not achieved.

Moreover, when an attempt is made to deposit the tungsten layer 114after the titanium nitride pieces 103 a, the tungsten layer 114 tends tostop short of filling the via, leaving a void 119 shown in FIGS. 1C and1D. The void 119 is filled with neither titanium nitride nor tungsten,such that there is a high likelihood that there will be no electricalconductivity from the metal 102 to the tungsten layer 114.

In view of the forgoing, there is an unfilled need for a reliablesemiconductor via structure, and a method of making reliable viastructures to prevent outgassing problems and associated via hole voids.

SUMMARY OF THE INVENTION

Broadly speaking, the present invention fills these needs by providingimproved semiconductor device via structures having an inner hydrophobicwall surface layer to prevent the aforementioned moisture absorption andsubsequent outgassing. Such via structures are made using techniques forconverting a silicon dioxide inner wall layer into the desirablehydrophobic layer, thus preventing the failure inducing voids in the viastructures. It should be appreciated that the present invention can beimplemented in numerous ways, including as a process, an apparatus, asystem, a device, or a method. Several inventive embodiments of thepresent invention are described below.

In one embodiment, a method of making a via hole in a semiconductorstructure is disclosed. The via hole has a surface layer of hydrophobicmaterial, and includes an outer layer of a material having acharacteristic of SOG materials. The characteristic is that the outerlayer oxidizes during photoresist ashing to form a surface layer ofsilicon dioxide in the via hole. In the method, an operation isperformed after the ashing. The operation includes performing a chemicaldehydroxylation operation on the surface layer of silicon dioxide toconvert the surface layer of silicon dioxide to the surface layer ofhydrophobic material. To achieve this, the semiconductor structure isplaced in a closed process chamber, and then, a halogen compound isadmitted into the process chamber to facilitate the chemicaldehydroxylation operation. In this embodiment, the halogen compound isselected from either NH₄F, other gaseous combination including fluorine,or CCl₄.

In an other embodiment, a method of malting a via hole in asemiconductor device is disclosed. The method includes defining a viahole having a wall surface that at least partially has a characteristicof spin on glass materials. The characteristic being that the wallsurface oxidizes during a photoresist ashing operation and the oxidizingconverts the wall surface into a silicon dioxide skin. The method thenincludes placing the semiconductor device in a process chamber. Once thesemiconductor device is placed in the process chamber, the methodincludes introducing a halogen gas into the process chamber to cause achemical dehydroxylation of the silicon dioxide skin to thereby convertthe silicon dioxide skin into a hydrophobic material skin, such that thehydrophobic skin is part of the wall surface of the via hole.

In still another embodiment, a semiconductor via structure that isconfigured to be defined through an inter-metal dielectric is disclosed.The structure includes a first conductive pattern element. A layer ofSOG material formed over the first conductive pattern element. The layerof SOG material having a via hole defined therethrough, such that thevia hole defines a path to the first conductive pattern element. The viahole has a via wall surface that is defined along the SOG material thatextends to the first conductive pattern element, and the via wallsurface has a hydrophobic material layer. In this embodiment, thehydrophobic material layer is a reaction product of silicon dioxide anda halogen compound. The halogen compound may be NH₄F or CCl₄, and whenthe CCl₄ is used, the via hole fill material that will be in contactwith the hydrophobic material layer is preferably copper.

As an advantage of each of such embodiments, no high temperatureoutgassing is required to avoid the disadvantages of the oxidized SOGlayer, e.g., the silicon dioxide layer that is formed in the SOG aftertypical ashing operations. Other aspects and advantages of the presentinvention will become apparent from the following detailed description,taken in conjunction with the accompanying drawings, illustrating by wayof example the principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be readily understood by the followingdetailed description in conjunction with the accompanying drawings.Therefore, like reference numerals designate like structural elements.

FIG. 1A is a cross sectional view of a prior art semiconductor structureshowing a via formed through a layer of SOG material at a locationdefined by photoresist;

FIG. 1B is a cross sectional view of the semiconductor structure shownin FIG. 1A after an ashing operation has been performed to remove thephotoresist, wherein an undesired surface layer of oxidized SOG materialis formed after the ashing operation;

FIG. 1C is a cross sectional view of the semiconductor structure shownin FIGS. 1A and 1B after an unsuccessful attempt to deposit a completelayer of titanium nitride, showing an undesired discontinuouscharacteristic of the titanium nitride caused by outgassing of theundesired surface layer of oxidized SOG material;

FIG. 1D is an enlarged view of a portion of the structure shown in FIG.1C, illustrating a void defined due to the failure of a tungsten layerto be deposited completely in the via hole surface walls due tooutgassing of moisture from the undesired surface layer of oxidized SOGmaterial;

FIG. 2A is a cross sectional view of the semiconductor structure shownin FIG. 1B, showing a process of the present invention including achemical dehydroxylation operation performed on the surface layer ofsilicon dioxide to convert the surface layer of silicon dioxide toprovide the surface layer of hydrophobic material of the presentinvention;

FIG. 2B is a schematic view of a process chamber in which the chemicaldehydroxylation operation is performed, showing the semiconductorstructure with the surface layer of silicon dioxide which is to beconverted to the surface layer of hydrophobic material of the presentinvention;

FIG. 2C is a schematic illustration of the process of converting thesilicon dioxide layer to the hydrophobic layer;

FIG. 2D is a cross sectional view of the semiconductor structure shownin FIG. 2A, showing a result of the process of the present invention asincluding the provision of the surface layer of hydrophobic material ofthe present invention;

FIG. 3A is a flow chart depicting operations of the process of thepresent invention; and

FIG. 3B is a flow chart illustrating sub-operations of a chemicaldehydroxylation operation shown in FIG. 3A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An invention for reliable via structures, and methods for makingreliable via structures in semiconductor devices, which circumvent theaforementioned problems of via voids and associated outgassing, isdisclosed. In a preferred embodiment, the reliable via structures aremade to have a via wall surface layer that is hydrophobic. As such, thevia wall surface layer will substantially not absorb moisture, which isa major contributing factor of conductive via voids. In the followingdescription, numerous specific details are set forth in order to providea thorough understanding of the present invention. It will beunderstood, however, to one skilled in the art, that the presentinvention may be practiced without some or all of these specificdetails. In other instances, well known process operations have not beendescribed in detail in order not to obscure the present invention.

FIG. 2A shows one embodiment of a chemical dehydroxylation operation ofthe present invention performed on the surface layer 106 of silicondioxide to convert such layer 106 to a hydrophobic material. Theoperation may be performed on SOG material of the layer 104, suchmaterial having the characteristic of spin on glass. The SOG material istaken from the group consisting of the true spin on glass describedabove, and the SOG-like material described above as including, forexample, an organic vapor-deposited low thermal expansion coefficientmaterial, and other spin coated low K dielectrics. Such SOG material ofthe layer 104 has the characteristic of spin on glass as shown in FIG.1C, and has the oxidized surface layer 106 of silicon dioxide. Thechemical dehydroxylation operation uses a halogen compound.

FIG. 2B shows an example chamber apparatus for performing the chemicaldehydroxylation operation in accordance with this embodiment. Thechemical dehydroxylation operation is performed by placing thesemiconductor structure of FIG. 2A in a closed process chamber 122. Itshould be noted that many types of chambers may be used, and one or morewafers may be placed in a chamber at one time. For example, when morethan one wafer is placed in the chamber in a batch, the wafers arepreferably held in a wafer carrier. A halogen supply 123 is configuredto be admitted into the closed process chamber 122, such that thehalogen compound is capable of facilitating the chemical dehydroxylationoperation. The preferred flow rate of the halogen supply is preferablyset between about 10 sccm and about 50 sccm, and most preferably set toabout 20 sccm. The halogen compound used in the chemical dehydroxylationoperation may be NH₄F or CCl₄, for example. Upon causing the chemicaldehydroxylation operation, by-product gases, such as, NH₃ and vapor H₂Oare believed to be formed. These by-product gases may then be removedfrom the chamber using any number of conventional techniques.

FIG. 2C schematically shows the reaction of surface OH groups (ie.,Si—OH) of the silicon dioxide of surface layer 106 with the NH₄F. Thesilicon dioxide of the layer 106 is shown reacting with the NH₄F, suchthat the fluorine (F) vapors replace the OH groups, and thereby resultsin a hydrophobic layer 121. The hydrophobic layer is thus Si_(S)F. Ofcourse, other fluorine containing gases may also be used to cause thereplacement of the OH groups and produce the hydrophobic layer 121.

FIG. 2D schematically depicts the result of the chemical dehydroxylationoperation, illustrating the hydrophobic layer 121 as a layer thatdefines the walls of the via hole. The hydrophobic layer 121 is shownhaving the fluorine (F) at the surface, instead of the porous OHinterface shown at the surface of the layer 106 in FIG. 2A.Significantly, FIG. 2D shows the titanium nitride layer 103 as being acontinuous layer which is permitted to be deposited in such continuousmanner against the surface of the hydrophobic layer 121. Further, FIG.2D shows the tungsten layer 114 filling the via hole substantiallyagainst the continuous surface of layer 103, and thereby making a goodelectrical contact with the first conductor 102.

A process of the present invention may include a series of operationsdepicted in FIG. 3A. The process may start with a structure such as thatshown in prior FIG. 1A, where an operation 132 spin coats thephotoresist layer 108 onto the silicon dioxide layer 107 to define theintended location and size of a via, or a plurality of vias of anintegrated circuit device. An operation 134 then etches the via hole orholes in the layers 104 and 107. An ashing operation 136 is performed toremove the photoresist and define the structure shown in FIG. 1B, andthe SOG layer 104 is exposed in operation 137 to atmosphere and becomesoxidized. As a result, the surface layer 106 becomes defined in the SOGlayer 104 as shown in FIG. 1B. Further processing is performed in anoperation 138 to remove side wall polymers (not shown) formed duringetching, for example. Such removal is typically done using a wet solventstripper.

To avoid the disadvantages of the prior art, the process of the presentinvention includes a chemical dehydroxylation operation 142, asdescribed above. In more detail, this operation 142 includessub-operations shown in FIG. 4B, including an admitting sub-operation144 by which the halogen compound is introduced into a closed processchamber 122. The admitting operation 144 is performed until the pressurein the chamber 122 is broadly from about 1.5 to 3.0 atmospheres, and ismore preferably from about 1.5 and about 2.0 atmospheres. In asub-operation 146, the temperature in the chamber 122 is controlled tobe from about 100 degrees C. to less than about 450 degrees C., and morepreferably from about 100 degrees C. to less than about 200 degrees C.,and most preferably at about 120 degrees C. In an operation 148, thechemical dehydroxylation operation 142 is performed for a period fromabout 0.5 to 6 minutes, and more preferably for a period of about 1minutes to about 3 minutes, and most preferably for 2 minutes. Theoperation 142, including the sub-operations 144, 146, and 148, resultsin the forming of the hydrophobic layer 121 shown in FIG. 2D, which isthe surface of the via hole onto which it is desired to deposit thetitanium nitride layer 103.

When the halogen compound used in the operation 142 is NH₄F, a physicalvapor deposition (PVD) operation 152 may be used to deposit thecontinuous titanium nitride layer 103 in the via hole or via holes,which results in a continuous, conductive layer being provided over andin contact with the hydrophobic layer 121 and in electrical contact withthe first conductor 102. In FIG. 2D, such continuous layer 103 isdistinguished from the discontinuous layer 103/103 a shown in FIGS. 1Cand 1D.

Then, in an operation 154, a chemical vapor deposition (CVD) operationmay be used to deposit the tungsten layer 114 in the via hole and indirect contact with the titanium nitride layer 103. The tungsten layer114 is also a continuous layer, that is, a layer that completely fillsthe via hole and that is in direct electrical contact with substantiallyall of the titanium nitride layer 103. Then, a chemical mechanicalpolishing (CMP) operation is used to planarize the top of the via holeof FIG. 2D. For example, the CMP operation will preferably remove theexcess tungsten material and TiN material down to the layer 107.Following the CMP operation, an operation 158 determines whether thereare any more semiconductor structures, i.e., conductive vias tofabricate at other layers of the semiconductor device. If thedetermination is yes, then a loop 160 is taken to operation 132, andsuch operation 132 is performed for the next via structure orstructures. If the determination is no, then after the operation 158,the operations ends.

A further embodiment of the present invention contemplates the halogencompound being CCl₄, rather than NH₄F in the chemical dehydroxylationoperation 142, and more specifically in the admitting operation 144. Inthis embodiment, in the operation 152, cooper is preferably used to fillthe via holes over the surface layer 121 of hydrophobic material. Afterthe copper layer, further operations may be performed as describedabove, resuming with operation 156.

It should be understood then, that an advantage of each of the describedembodiments is that no high temperature outgassing is required to avoidthe disadvantages of the porous surface layer 106 of silicon dioxide.Instead of such undesired high temperature outgassing, the layer 106 isconverted into the hydrophobic layer 121, which thus allows the titaniumnitride materials, copper materials, aluminum materials, or any othertype of via fill metallization to be properly deposited in the via hole.Thus, the resulting via hole structures will be substantially morereliable than conventional via structures.

Although the foregoing invention has been described in some detail forpurposes of clarity of understanding, it will be apparent that certainchanges and modifications may be practiced within the scope of theappended claims. Accordingly, the present embodiments are to beconsidered as illustrative and not restrictive, and the invention is notto be limited to the details given herein, but may be modified withinthe scope and equivalents of the appended claims.

What is claimed is:
 1. A semiconductor via structure being definedthrough an inter-metal dielectric, comprising: a first conductivepattern element; and a layer of SOG material formed over the firstconductive pattern element, the layer of SOG material having a via holedefined therethrough, such that the via hole defines a path to the firstconductive pattern element, wherein the via hole has a via wall surface,the via wall shape is defined along the SOG material that extends to thefirst conductive pattern element, and the via wall surface has ahydrophobic material layer.
 2. A semiconductor via structure beingdefined through an inter-metal dielectric as recited in claim 1, whereinthe hydrophobic material layer is a reaction product of silicon dioxideand a halogen compound.
 3. A semiconductor via structure being definedthrough an inter-metal dielectric as recited in claim 2, wherein thehalogen compound is NH₄F.
 4. A semiconductor via structure being definedthrough an inter-metal dielectric as recited in claim 2, wherein thehalogen compound is CCl₄.
 5. A semiconductor via structure being definedthrough an inter-metal dielectric as recited in claim 3, furthercomprising: a layer coating the via hole in direct substantiallycontinuous contact with the hydrophobic material layer, the layercoating being a titanium nitride material.
 6. A semiconductor viastructure being defined through an inter-metal dielectric as recited inclaim 5, further comprising: a conductive fill material contained withinthe via hole and in direct substantially continuous contact with thelayer coating.
 7. A semiconductor via structure being defined through aninter-metal dielectric as recited in claim 6, further comprising: asecond conductive pattern element in conductive contact with theconductive fill material, the titanium nitride material, and the firstconductive pattern element, thereby defining a reliable conductiveinterconnection between a first metal layer network that includes thefirst conductive pattern element and a second metal layer network thatincludes the second conductive pattern element.
 8. The semiconductor viastructure of claim 1, further comprising a dielectric layer positionedon the layer of SOG material, the dielectric layer being positioned overthe hydrophobic material layer.
 9. The semiconductor via structure ofclaim 1, wherein the layer of SOG material and the dielectric layer eachinclude silicon dioxide and the hydrophobic material layer includeshalogen atoms bonded to silicon atoms.
 10. A semiconductor apparatus,comprising: a substrate; a conductor positioned on the substrate; afirst dielectric layer in contact with at least a portion of theconductor; a second dielectric layer on the first dielectric layer; anda via defined through the first dielectric layer and the seconddielectric layer, the first dielectric layer including a hydrophobicmaterial portion defining a via wall, the hydrophobic material includinghalogen atoms bonded to silicon atoms; and a metal layer positioned onthe second dielectric layer and extending into the via to electricallyconnect to the conductor.
 11. The apparatus of claim 10, wherein thefirst dielectric layer and the second dielectric layer include silicondioxide. between the metal layer and the second dielectric layer. 12.The apparatus of claim 10, further comprising an electrically conductivelayer between the metal layer and the second dielectric layer.
 13. Theapparatus of claim 12, wherein the metal layer includes tungsten and theconductive layer includes titanium nitride.
 14. The apparatus of claim13, wherein the halogen atoms are fluorine atoms.
 15. The apparatus ofclaim 10, wherein the halogen atoms are chlorine atoms and the metallayer includes copper.
 16. An apparatus, comprising: a chamber; ahalogen supply to provide a halogen-containing gas to the processingchamber, a semiconductor device positioned in the chamber, thesemiconductor device including: a substrate; a conductor formed on thesubstrate; a first dielectric layer positioned on the conductor; asecond dielectric layer positioned on the first dielectric; and whereinthe first dielectric layer and the second dielectric layer define a viahole; a via hole wall surface of the first dielectric layer including aporous material of silicon bonded to hydroxyl groups indicative of a SOGdielectric material, porosity of a via hole wall surface of the seconddielectric layer is greater than the first dielectric layer, and theprocessing chamber and the halogen supply are controlled to cause areaction between the halogen-containing gas and the porous material toprovide a hydrophobic material by exchanging the hydroxyl groups withhalogen atoms.
 17. The apparatus of claim 16, wherein the dielectriclayer and the second dielectric layer each include silicon dioxide andthe halogen-containing gas is in the form of CCl₄ or NH₄F.